Administration of bisphosphonate (ibandronate) impedes molar tooth movement in rabbits: A radiographic assessment.

INTRODUCTION: Bisphosphonate (Bp)-ibandronate is a pharmacological agent, exhibits antiosteoclastic or antiresorptive activity and used to treat osteolytic or osteopenic disorders. BP-ibandronate may also interfere during orthodontic tooth movement. The aim of this study was to examine the influence of locally administered Bp-ibandronate on experimental tooth movement in rabbits.
MATERIALS AND METHODS: Twenty rabbits were divided into two groups- "10" served as Group-1 (control) and other "10" as Group-2 (experimental). Both groups received nickel-titanium closed coil springs with 100 g force between mandibular molar and incisors. Group-1 animals received 1 ml normal saline and Group-2 animals received ibandronate solution (0.3 mg/kg body weight) locally, mesial to the mandibular molar on the 1(st), 7(th), and 14(th) day of the experiment. A total of "40" lateral cephalograms were taken from both groups on the 1(st) and 21(st) day using a digital X-ray unit (Siemens X-ray systems, 300 mA Pleomophos analog, 2008, Germany). Individually, each animal's radiograph was traced manually and superimposed. The molar tooth movement was measured with the help of a standard metric scale.
RESULTS: The Student's t-test has been done to compare the mean values of Group-1 (4.650 ± 0.363) and Group-2 (2.030 ± 0.291) and the difference was statistically significant (P < 0.001).
CONCLUSION: The retarded molar tooth movement was noticed in local drug administered rabbits, which could be beneficial in orthodontics to control the undesired tooth movement.

Orthodontic tooth movement (OTM) is made possible by the application of constant force on a tooth using mechanical devices such as springs, elastics, arch wires, screws, etc., During OTM, the periodontal ligament (PDL) and the alveolar bone undergo a wide range of remodeling process that is, selective deduction of bone on the pressure side (resorption) and the addition of bone on the opposite side (apposition). Several chemical mediators, cytokines, and inflammatory mediators also play an important role during OTM.[1] The remodeling of PDL tissue is a core factor for OTM.

In orthodontic patients, the intake of various medications might affect the OTM in a negative manner (deceleration of OTM) or positive manner (acceleration of OTM). NSAIDs (diclofenac sodium,[2] indomethacin,[3] acetyl salicylic acid,[4] ibuprofen[5]), leukotrienes antagonist - zileuton,[6] phenytoin,[7] bisphosphonates (Bps),[891011121314151617181920] etc., are some important medical agents accountable for deceleration of OTM; contrary, local administered vitamin D,[21] parathyroid hormone hormones,[22] prostaglandins,[23] cytokines,[24] corticosteroids[25] (long-term use and dose dependent manner), etc., are accountable for acceleration of OTM.

Bisphosphonates are a group of medications developed in the mid-19th century and widely used in the management of skeletal metabolic disorders such as osteoporosis, malignant bone metastatic conditions, Paget's disease, osteogenesis imperfecta, etc.[2627] Before invading into medical application, they were used in textile and fertilizer industries as anticorrosive agents to prevent the formation of calcium carbonate deposits in the pipe lines.[28]

Bisphosphonates are synthetic analogs of inorganic pyrophosphate. Pyrophosphates are present profusely in the body fluids including saliva; they have two phosphonate (PO3) groups linked with an oxygen molecule (P-O-P). The synthetic Bps have a similar structure, but the oxygen molecule is replaced by the carbon. The substitution of carbon for oxygen in Bp gives maximum resistance to thermal, chemical and enzymatic degradation and increase bone matrix accumulation and extreme long half-life. The carbon is linked with the long chain (R2) and short chain (R1); R2 determines the potency and R1 determines the chemical properties and pharmacokinetics [Figure 1].[27]

Figure 1

Structure of inorganic pyrophosphate (left) contains oxygen atom and its synthetic analogue bisphosphonate (right) where the oxygen atom is replaced with carbon atom

Bisphosphonates are categorized into nonnitrogenous group or basic type (clodronate, etidronate, and tiludronate) and nitrogenous group (alendronate, pamidronate, risedronate, ibandronate, zoledronate, etc.). The presence of the nitrogen atom increases the drug potency. Both groups of Bps act in different pathways, but eventually they exhibit antiosteoclastic activity. Nonnitrogenous Bps incorporates into nonhydrolysable analogs of adenosine triphosphate (ATP), interfering with ATP-dependent pathways and resulting in osteoclast apoptosis,[27] whereas nitrogenous Bps inhibits the enzyme of the mevalonate pathway called farnesyl pyrophosphate synthase, which in sequence inhibits the enzymatic modification of small guanosine triphosphate-binding proteins in osteoclasts and interrupts the cytoskeletal function and intracellular signaling, which triggers the osteolytic action and ultimately leads to osteoclast apoptosis.[2728] Apart from antiosteoclastic activity, Bps also expresses the antiangeogenic effect (antivascular effect) by obstructing endothelial growth factor.[29]

Once Bp enters the circulation 50% of the drug is excreted through urine. The bioavailability of oral administered Bps is low (1-10%), when compared with intravenous administered Bps (up to 50%).[26] The higher amount of Bps accumulates in the human jaws (10 times higher than other bones), because the greater amount of remodeling occurs during regular mastication process.[30] The lethal adverse effect of Bp pertained to dentistry that is, “osteonecrosis of the jaw” (ONJ) or “bisphosphonate related osteonecrosis of jaws (BRONJ), was documented by Marx in 2003,[31] has alarmed the entire dental fraternity all over the world. The possible linkages between the occurrence of ONJ and Bp therapy, could be due to the antiosteoclastic activity,[28] antiangiogenic activity,[29] compromised blood supply to the jaw bones in Bp recipients,[30] augmented bone density due to the suppression of bone resorption,[26] etc., In Bp users, any general dental procedures and orthodontic procedures should be carried out with a special consideration because of the possibility of occurrence of BRONJ. The major general dental procedures (extractions, implants, surgeries, etc.) and orthodontic procedures (extraction therapies, excessive force application, attempt to treat major malocclusions, etc.) should be avoided and conservative management is advocated.[3233] Until date, there is no evidence of BRONJ was recorded in orthodontic patients along with Bp usage; but in such patients, the prior conditions to BRONJ such as sclerotic zones in the alveolus, widened PDL, hyper mineralized areas in the extraction sites, etc., were reported and eventually resulted with some undesirable effects such as an impediment of OTM, difficulty in extraction space closure, compromised root parallelism, etc.[33]

In orthodontic terminology, the anchorage is explained as the resistance acquired by the tooth/teeth against (usually molars) the OTM. Usually, molars are multirooted teeth, which offer better anchorage, and to augment the effect of anchorage certain components (trans palatal arch, Nance arch, etc.) are attached to the molars. Apart from these mechanical anchorage devices, investigators have been trying to generate a “pharmacological anchorage method,” as an alternative approach that is, local administration of certain drugs (particularly Bps) near to the tooth/teeth are intended to produce resistance against OTM,[8910111213] and to facilitate OTM of the desired tooth/teeth.

In this study, Bp-ibandronate, a Nitrogenous Bp was used. The chemical name for ibandronate is (1-hydroxy-3-[methylpentlyamino] propylidene) bis-phosphonic acid, monosodium salt, monohydrate with the molecular formula C9H22NO7P2Na H20 and a molecular weight of 359.24. The aim of this study is to examine the effect of Bp-ibandronate on OTM in rabbits following local administration using lateral cephalic radiographs.

Materials and Methods

Animal model

Twenty New Zealand rabbits, 16-week-old, weighing between 3.5 and 4 kg (3.75 kg mean weight) were chosen for this experiment. This animal experiment was carried out in accordance with the guidelines issued by Institutional Animal Ethics Committee of Annamalai University, Tamil Nadu, India, with an approval code CPCSEA 169/99, proposal No. 854. All rabbits were segregated into two groups’ that is, Group-1 (control) and Group-2 (experimental). The general health status of each animal was monitored throughout the phase of the experiment by us and the veterinarian staff. Animals were fed with nutritional diet supplied in pallets, which were crushed into small pieces to prevent damage to the orthodontic appliance (nickel-titanium [NiTi] coil spring). Throughout the study, the animals were kept under conditions of room temperature between 24°C and 26°C.

Pharmacological agents used

Ketamine (50 mg/kg body wt) along with diazepam (5 mg/kg body wt) and atropine (0.2 mg/kg body wt) intramuscular injection were used for anesthesia. The Bp-ibandronate, (injection bandrone, 6 mg/6 ml vial supplied by Arihanth Medi Pharma, Chennai, India) was used as an experimental drug. Ibandronate 0.3 mg/kg body weight was administered locally that is, mesial to the rabbit's mandibular molar in the mucoperiosteum region.

Orthodontic force element

In this experiment, both animal groups have received sentalloy NiTi closed coil springs with 100 g force NiTi (GAC International, New York). This coil spring was stretched and ligated between the mandibular molar and incisors [Figure 2].[3435]

Figure 2

Experimental animal with the appliance in place and local drug administration

Experiment technique

The duration of the experiment was carried out for 21 days. On the 1st day, animals received the appliance under anesthesia. A specially designed mouth prop was placed following application of anesthesia. The grooves were made around the cervical margins of molar and incisors. A ligature wire of 0.009” was passed around the mandibular first molar with the help of artery forceps. The stainless steel ligature wire was knotted mesial to the molar and both ends of wire were passed into the coil spring and twisted, the excess wire was cut and the projected wire was bent toward the cervical margin of the molar. The other end of the spring was stretched with the help of an electronic force gauge (LT Lutron FG 5000A Taiwan) at the 100 g force level and ligated around the incisor. Circumferentially ligature wires were seated into the grooves at both ends (cervical margins of incisors and molars). These cervical margins were etched with 37% phosphoric acid and coated with light cure composite material (3M Transbond XT primers and the composite 3M unit) in order to secure the appliance without dislodgment and also minimize the irritation caused by the wire projections.

All control animals (Group-1) received 1 ml normal saline and correspondingly experimental animals (Group-2) received Bp-ibandronate of 0.3 mg/kg body weight on the mesial aspect of rabbit's mandibular first molar into the mucoperiosteum for 3 times (1st, 7th and 14th day) [Figure 2]. In a while, all animals were exposed to radiography to acquire cephalic radiographs on the 1st day along with appliance under anesthesia and on the 21st day along with application under anesthesia [Figure 3].

Figure 3

Digital X-ray unit (Siemens X-ray systems, 300 mA Pleomorphism analog, 2008, Germany)

Lateral cephalic radiographs

Both groups of animals were exposed to radiation individually on the 1st and 21st days, and totally “40” lateral cephalic radiographs were produced using method previously described. The cephalic X-ray films were exposed using a digital Siemens 300 mA Pleomorphism analog digital X-ray unit. The exposure time (0.4-0.5 s) and the power settings (60-70 kV, 10 mA) were standardized to all animals. The X-rays were taken with the left side of the head of the animal facing the X-ray tube at a standardized distance of 60 cm away from the tube with animal lying in a supine position [Figure 3]. This technique has been adopted from the previous study.[36] Cephalic radiographs were traced manually using acetate paper and land marks were pointed with micro tip lead pencil [Figure 4]. Individually each animal's lateral cephalic radiographs were superimposed and the magnitude of molar tooth movement in the mesial direction was measured manually using standard metric scale based on two reference points that is, a mesio-occlusal tip of the second molar (M1) to the disto-occlusal tip of the first molar (M2) [Figures 5 and 6].

Figure 4

Land marks in cephalic radiograph-Na (Nasion), Pa (Parietal bone), Oc (Occipital bone), T (Temporal bone), IL (Incisal tip of lower incisor), M1 (disto-occlusal tip of first mandibular molar), M2 (mesio-occlusal tip of second mandibular molar)

Figure 5

Superimposed radiographic tracing of Group-1 (control) showing greater amount of molar tooth movement (distance between M1 and M2)

Figure 6

Superimposed radiographic tracing of Group-2 (experimental) showing lesser amount of molar tooth movement (distance between M1 and M2)

Results

Statistical analysis - the measured values (in millimeters) collected from both groups following radiographic tracing and superimposition are tabulated [Tables 1 and 2]. The mean values between two groups were compared by the Student's t-test. According to this test, it is considered to be statistically significant different between two groups if the P < 0.05. In this study, the mean values of Group-1 (control) (4.650 ± 0.363) and Group-2 (experimental) (2.030 ± 0.291) have shown clear demarcation that is, Group-2 is lesser than the Group-1, and the difference between these two groups was found to be statistically significant (P < 0.001) [Table 2]. The result of the current study has declared that the Group-2 (experimental) animals have shown significant reduction in the magnitude of molar tooth movement than Group-1 (control) [Table 2 and Graph 1].

Table 1

Measurements-obtained from superimposed radiographs (all measurements in millimeters)

Table 2

Students t test to assess the mean variation between the two groups (n=10)

Graph 1

The statistical result shows that the calculated P value (P < 0.05) is significant at 0.001 level. The significant difference in molar tooth movement is shown in the graph

Discussion

In this study, locally injected Bp-ibandronate has markedly decreased molar tooth movement in the mesial direction which could be due to the expression of the antiresorptive activity (antiosteoclastic activity) in the mesial aspect of molar.[28] Based on previous experiments, it is clearly evident that the locally delivered drugs near to the tooth/teeth structure express its action effectively in impeding tooth movement.[8910111213] In this study also, the readily available Bp-ibandronate at the local site (mesial to the molar), would’ve taken up by the osteoclasts after stimulation of bone turnover due to the OTM; than the mevalonate pathway is disrupted by the inhibition of farnesyl pyrophosphate synthetase and geranylgeranyl pyrophosphate enzymes, decreased cytoskeletal integrity and intracellular signaling; eventually apoptosis might have taken place in the local site.[28] In this study, the lateral cephalic radiographs were taken for each animal successively on the 1st and 21st day, individual animal's radiographs were superimposed and the molar tooth movement was measured manually with metric sale. The position and the distance of the rabbit's head from the X-ray source (70 mm) was constantly maintained in accordance to a similar previous study done by Bryndahl et al.[36] Furthermore, the intra oral installation of appliance[3435] and local administration of the drug[8910111213] have been followed from earlier studies.

The basis behind the local Bp administered studies in animals[8910111213] were to determine the possibility of utilizing the adverse effect of Bps (impediment of tooth movement) in a favorable manner to enhance the resistance of that particular tooth/teeth and to move the other teeth effectively.

Igarashi et al. and Adachi et al.,[810] examined the effect of 4-amino-1-hydroxybutylidene-1,1-bisphosphonate on OTM following local administration in rats. In this experiment, significant reduced molar tooth movement during expansion and also lesser amount of relapse were noticed following withdrawal of the expansion force which could support the pharmacological induced anchorage and retention phenomenon. In another similar study, Igarashi et al. 1996[9] have noticed that the topically administered risedronate might be useful in impeding root resorption during OTM following withdrawal of (expansion) orthodontic force. In the current study, limited molar tooth movement was observed in the superimposed lateral cephalic radiographs of local Bp-ibandronate administered animals, which could have hindered the resorption process in PDL by the drug.

Fujimura et al.[12] investigated the effect of Bp in mice after injecting into a site adjacent to the maxillary molar and observed reduction in the tooth movement, number of osteoclasts and root resorption in Bp administered animals than the nondrug administered group. Liu et al.,[11] in a rat split mouth study administered clodronate locally close to the molars and found a significant diminution in tooth movement, which is dose dependent. On the experimental side, there is a reduced amount of osteoclasts compared with the control side. In this study at the end of 3rd week, the local Bp-ibandronate received rabbits have shown a reduced movement of molar tooth, which is statistically significant. This decrease in tooth movement could be due to the expression of antiosteoclastic activity of the drug in the locally injected site.

Venkataramana et al.,[13] in a 21 days study on albino rabbits used Bp – Pamidronate as a local injection mesial to the mandibular molar and demonstrated a reduction in mesial molar tooth movement on dissected mandibles and also by osteoclastic quantification. They finally suggested that the locally injected Bp – Pamidronate might be useful to augment the anchorage in future days. In the current study, Bp-ibandronate has also shown the similar effect as pamidronate in reducing tooth movement on local administration.

Apart from local Bp administered studies, some authors have studied the effect of systemic administered Bps[14151617181920] in animals during OTM. In these studies, chiefly investigators have noticed impediment of tooth movement and depletion in osteoclastic count, which could be clinically applicable to the Bp using patients undergoing an orthodontic treatment[2324] and a special consideration to be given to them. They also suggested that the OTM was inhibited due to the interruption of Bps; this deleterious effect could be utilized in a positive manner on local administration in the future era to restrict (or) control the undesired tooth movement, and to facilitate desired tooth movement.

Ibandronate (nitrogenous Bp) is used in this study because it is more potent than other nitrogenous Bps (except zolendronate) in inhibiting bone resorption,[37] thereby OTM is very well-prevented in local Bp administered animals. In orthodontics, this could be considered as a positive event in terms of producing “pharmacological anchorage method” or “drug-induced anchorage” by local administration.

Conclusion

In the current study, Bp – Ibanronate has been administered locally in order to study its effect on molar tooth movement in rabbits and the significant reduction in the molar tooth movement was noticed, which was elucidated using lateral cephalic radiographs. Bp-ibandronate is an antiresorptive agent and on its local administration it has prevented molar tooth movement in rabbits, which is an unfavorable action in orthodontic perspective. However, in the clinical scenario pertained to orthodontic specialty, this unfavorable action may be utilized to prevent unwanted tooth movement (particularly molar teeth) and to enhance “Pharmacological Anchorage Method” with a local administered drug. Unfortunately, until date this method is confined to animal studies and further studies are obligatory to apply this method in clinical orthodontics.